Process for treating elastomeric fibers

ABSTRACT

AN IMPROVED ELASTOMERIC FIBER AND METHOD FOR PRODUCING THE SAME ARE DISCLOSED AND CLAIMED WHICH METHOD COMPRISES STABILIZING THE CRYSTALLINE STRUCTURE OF A SPUN ELASTOMERIC FIBER BY TREATING THE FIBER WITH A SWELLING SOLVENT THEREOF WHILE MAINTAINING THE FIBER IN A STATE OF STRESS. PREFERABLY, THE FIBERS TREATED ARE SEGMENTED ELASTOMERIC COPOLYMERS. THESE PREFERRED ELASTOMERIC FIBERS ARE PREFERABLY POLYURETHANE-CONTAINING POLYMERS. THE RESULTING FIBERS HAVE IMPROVED PHYSICAL PROPERTIES PARTICULARLY AS MEASURED IN REDUCED PERMANENT SETTING CHARACTERISTICS.

United States Patent Oflice Patented May 16, 1972 3,663,677 PROCESS FOR TREATING ELASTOMERIC FIBERS Herbert W. Keuchel, Summit, N.J., assignor to Celanese Corporation of America, New York, N.Y.

No Drawing. Continuation of application Ser. No. 377,074, June 22, 1964. This application July 13, 1970, Ser. No. 56,191

Int. Cl. B29c 25/00 US. Cl. 264-210 F 5 Claims ABSTRACT OF THE DISCLOSURE An improved elastomeric fiber and method for producing the same are disclosed and claimed which method comprises stabilizing the crystalline structure of a spun elastomeric fiber by treating the fiber with a swelling solvent therefor while maintaining the fiber in a state of stress. Preferably, the fibers treated are segmented elastomeric copolymers. These preferred elastomeric fibers are preferably polyurethane-containing polymers. The resulting fibers have improved physical properties particularly as measured in reduced permanent setting characteristics.

This is continuation of Ser. No. 377,074, filed June 22, 1964, and now abandoned.

This invention relates to a process for producing improved elastomeric fibers. More particularly, this invention relates to the preparation of segmented elastomeric copolymers exhibiting enhanced characteristics of low permanent set.

Synthetic elastic fibers, the so-called stretch fibers, have generally received widespread public acceptance. The properties of these fibers, such as elasticity and a desirable hand or feel, make the stretch fibers highly suitable for the preparation of fibers for apparel and like products. However, these fibers have, in the past, been characterized by several undesirable features. Thus, for example, some elastomeric fibers, as spun, have shown a high degree of permanent set. A high permanent set, of course, is undesirable in wearing apparel where it is sought to obtain fabrics which will readily conform to the shape of the wearer and which will nevertheless maintain a high degree of elasticity.

"It is an object of this invention to provide a method for preparing fibers having low permanent set. It is a further object of this invention to provide a method for producing stretch fibers of segmented elastomeric copolymers, said fibers similarly being characterized by low permanent set. It is a still further object of this invention to provide a method whereby elastomeric fibers exhibiting a wide range of extensibilities and tenacities can be prepared. Other objects and the advantages of this invention will be apparent from the following detailed description and claims.

It should be noted that, although reference is made herein primarily to segmented elastomeric fibers, my invention is also applicable to other types of elastomeric fiber, such as, for example, those fibers derived from polyurethane-based polymers.

In accordance with this invention, elastomeric fibers are contacted with swelling solvents while said fibers are maintained in various states of stress. The fibers produced by this method are characterized by an extremely low permanent set. In addition, the properties of these fibers can be further enhanced by further subjecting the fibers to a heat setting or heat treating step subsequent to the solvent contacting step.

The fibers suitable for treatment in accordance with the process of my invention are preferably segmented, elastomeric copolymers and can 'be spun by any of the methods well known in the art, e.g., dry spinning, wet spinning or melt spinning.

The term segmented, elastomeric copolymers, as said throughout this specification and in the claims, is meant to describe elastomeric copolymers comprised of two principal types of segments which are chemically connected and alternate in the chemical chain. One segment, preferably essentially amorphous, may be derived from low melting soft polymers, such as, for example, an ester polymer, an ether polymer, a hydrocarbon polymer or the like. Such soft polymers are characterized by relatively weak inter-chain attractive forces. The other segment is derived from a hard high melting polymer, such as, for example, a urea polymer, a urethane polymer, an amide polymer or the like. In particular, the soft segments of these elastomers are derived from low melting polymers having a melting point below about 60 C., having a molecular weight of from about 250 to about 5000 and containing terminal radicals possessing active hydrogen atoms. The hard, high melting segments are generally derived from linear hard polymers having a melting point above about 200 C. in their fiber forming molecular weight range, i.e., above about 5000. The soft segments, as present in the elastomer, appear as radicals of the initial polymer from which the terminal active hy drogens have been removed. Generally, the hard segments comprise from about 10% to about 40% by weight of the segmented copolymer and may be defined as comprising at least one repeating unit of the linear polymer from which they are derived.

As mentioned previously, the fibers derived from the segmented elastomeric copolymers are subjected to the action of a swelling solvent while the fibers are maintained under various degrees of stress. The fibers may be contacted with the swelling solvent by any means convenient to the practitioner, such as, e.g., immersion or spraying.

The stress to be applied to the fibers may vary considerably according to the nature of the fibers treated as well as to the characteristics desired to be produced in the finished fibers. According to the process of my invention, the fiber as spun may be treated, e.g., in a relaxed state, i.e., while it is maintained at zero strain and is therefore free to shrink; or, the fiber may be treated while it is maintained at constant length; or, the fiber may be treated under stress whereby the fiber is stretched as much as from 450 to 500% over the initial length of the fiber. As far as treatment under stress suificient to cause the strain in the fiber is concerned, it is preferred to use stresses resulting in stretching of the fiber up to about 200% over the initial length of the fiber.

While slight variations in the fiber characteristics obtained by the process of my invention results from treatment at different temperatures, there is no critical temperature range required in order to realize low permanent set properties. It is preferred, however, that the solvent contacting be carried out at a temperature below the boiling point of the particular solvent being utilized.

The solvent which may be utilized in the process of my invention to treat the elastomeric fibers include, among others, such swelling solvents as: the lower alkyl alcohols, e.g., methanol, ethanol and propanol; halogenated aliphatic hydrocarbons, e.g., methylene chloride and ethylene chloride; substituted aromatic hydrocarbons, e.g., chlorobenzene, N,N-dimethyl aniline, and nitrobenzene; ketones, e.g., acetone and methyl ethyl ketone; blends of alkyl alcohols and halogenated hydrocarbons, e.g., methanol-methylene chloride blends; blends of acetone and water; and the like. In general, the solvents applicable in the process of my invention may comprise any organic solvent which has a swelling effect on the elastomeric fibers treated, but which does not fully dissolve said fibers. It should also be noted that solvents which would ordinarily dissolve the elastomeric fiber could be utilized in the process of my invention by admixing such solvents with suitable non-solvents and thereafter implying the resulting blend to swell the fibers. I have found that solvents such as methanol and methanolmethylene chloride blends having weight ratios of from 64:36 to 37:63 are particularly suitable for attaining fibers of low permanent set by means of my procedure.

I have also found that the characteristics of elastomeric fibers can be further enhanced by subjecting the fibers to a heat-setting or heat-treating step subsequent to the solvent contacting step described hereinabove. The post-heating step is generally efifected at a temperature of from about 75 C. up to the softening point of the fiber and preferably at a temperature of from about 100 C. to about 150 C.

The length of time the fiber is subjected to heating, in accordance with this invention, can vary from a few minutes up to several hours. Generally it is preferred to subject a fiber to high temperatures for short periods of time or to low temperatures for extended periods.

In effecting the heat treatment aspect of my invention, the fibers as spun may be Wound, for example, on perforated metal bobbins at the desired stress level, and the bobbins thereafter dipped into a bath of the swelling solvent for a suitable length of time as desired by the practitioner. The treated fibers are then dried in air at room temperature before being exposed to elevated temperatures, for example, in a hot-air convection oven. If desired, the above-described sequence of solvent and heat treatment may be repeated several times with the same fibers.

In another embodiment of my invention, the elastomeric fiber is first stretched to at least about 150% of its initial length, relaxed to a length less than its stretched length, contacted with a swelling solvent therefore while maintaining the fiber in a state of stress, and heating the fiber at a temperature of from about 75 C. to a temperature below the softening point of the fiber. Alternatively, the elastomeric fiber may be subjected to solvent treatment while in a relaxed state or while it is maintained at constant length, the fiber thereafter being heat treated as described previously.

In the stretching step of the above mentioned embodiment, a stretch of at least 150% and usually in the range of from 200% to 500% over the initial length of the fiber, that is, the length of the fiber in its unstretched state prior to any treatment, imparts desirable characteristics to the fibers when employed in conjunction with the remainder of my process. Preferably, the amount of stretch employed is from about 250% to about 400%. The period of time during which the fiber is maintained in a state of stretch is not critical to my invention and can vary from periods of from less than one second to periods of several minutes. Usually the stretching can be conducted at about room temperature. The relaxing step which follows the stretching step described immediately above can be conducted at the same temperatures as the stretching step. The period of time during which the fiber is maintained in the relaxed state is not critical to my invention.

In the heating step of this aspect of my invention, temperatures from about C. to a temperature below the softening point of the fiber have generally been found to be effective. Usually a temperature of from about C. to about C. is adequate to develop desirable characteristics in elastomeric fibers produced from segmented elastomeric copolymers. The length of time a fiber is subjected to this heating step may vary from a few minutes to several hours.

As was mentioned previously, my invention is preferably applied to segmented elastomeric copolymers. The preparation of these segmented elastomeric copolymers is Well known in the art and is described, for instance, in U.S. Pats. Nos. 2,625,535; 2,813,776; 2,871,218; 2,953,839; 2,957,852; 2,962,470 and reissue 24,691.

The polymeric structure of some of these elastomers can be represented by the formula:

err-se wherein H and S denote the hard and soft segments, respectively; and wherein H is further represented by wherein Q is a divalent radical derived by reaction of an organic diisocyanate with active-hydrogen-containing functional groups; G is the residue resulting from the removal of active hydrogen from the terminal functional groups of a low molecular weight bifunctional molecule having a molecular weight less than 500; x is an integer or zero; b is an integer greater than zero; S is the residue resulting from the removal of the active hydrogen from the terminal functional groups of a polymer melting below 60 0, having a molecular weight of from about 250 to about 5,000. Terminal functional groups possessing active hydrogen can be, for example, OH, NH-,,, 4H, -COOH, CONH =NH, CSNH SO NH and SO OH. The hard segment in a repeating unit of a linear polymer may be further defined as having a melting point above about 200 C. in its fiber forming molecular weight range.

Generally, these synthetic elastomers are copolymer formulations based on low molecular weight aliphatic polyesters or polyethers having terminal hydroxyl and/0r carboxyl groups which are capable of further reaction with diisocyanates. This latter reaction can be used to couple the lower molecular Weight polyester or polyether via urethane links or the diisocyanate can be used in excess so that it becomes a terminal group. In this latter case, the macro diisocyanates formed can be coupled by means of other reagents such as water, diols, amino alcohols and diamines with the subsequent formation of the high polymer. These elastomeric products are also known as block copolymers.

A variety of organic diisocyanates may be used to pre pare the elastomeric copolymers suitable for employment in our invention. Illustrative examples of these diisocyanates are: trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, cyclopentylene 1,3 diisocyanate, 1,4-diisocyanate cyclohexane, pphenylene diisocyanate, m-phenylene diisocyanate, the tolylene diisocyanates, the naphthalene diisocyanates, 4,4-diphenyl propane diisocyanate, 4,4-diphenylmethane diisocyanate.

Illustrative of the types of elastomeric copolymers suitable for employment in our invention are isocyanate modified polyesters such as those described in U.S. Pat.

2,755,266 wherein linear polyesters prepared from poly car boxylic acids and polyhydric alcohols are reacted with an excess of a diisocyanate over the terminal hydroxyl groups of the polyester to form diisocyanate modified polyesters containing terminal isocyanate groups which are then further reacted with a bifunctional cross-linking agent. Polyesterurethane copolymers which are substantially free of cross-links, such as those described in U.S.- Pat. 2,871,218 wherein a critical ratio of an essentially linear hydroxyl terminated polyester prepared from a saturated aliphatic glycol having terminal hydroxyl groups and a dicarboxylic acid or its anhydride, and a diphenyl diisocyanate are reacted in the presence of a saturated aliphatic free glycol having terminal hydroxyl groups so that no unreacted isocyanate and hydroxyl groups remain, can also be employed. Broadly such a copolymer is obtained by reacting one mole of polyester with from 1.1 to 3.1 moles of a diphenyl diisocyanate in the presence of from about 0.1 to 2.1 moles of free glycol. Another type of elastomeric copolymer which can be used in our invention is the type described in U.S. Pat. 2,957,852. An elastomer of this type can be prepared by providing polyether glycol with isocyanate ends by reaction with a diisocyanate. This capped prepolymer can then be reacted with a chain-extending agent such as a hydrazine which provides a final polymer having repeating units containing hydrazine resins linked through carbonyl groups.

1 have further found that treatment of fibers with swelling solvents, as well as such treatment followed by heat setting, can also be applied to elastomeric fibers spun from blends of comparatively flexible and comparatively stilt segmented elastomeric copolymers. The flexibility or stiffness of two elastomeric copolymers is determined by the ratio of the amount of polyurethane to polyester or polyether in the block copolymersthe more flexible being that which has a greater proportion of the soft polymer.

In this aspect of my invention, the copolymers of the blend are segmented elastomeric copolymers of the type described previously. For example, both the stiff and the flexible copolymers can be synthesized from substantially the same starting material or at least starting materials of the same type. Thus, a soft or flexible copolymer of the type described in US. Pat. 2,871,218 can be produced by employing as starting materials larger proportions of the linear polyester and the aliphatic glycol, thereby producing a segmented copolymer having a greater number of amorphous or soft blocks. Similarly, a high molecular weight amorphous polymer employed as a starting ma terial will provide a copolymer having longer soft blocks. To obtain a comparatively stiff copolymer a larger pro portion of the diisocyanate, the linear crystalline component, can be employed thereby producing a segmented copolymer having a larger number of rigid blocks or a copolymer having longer rigid blocks, depending upon the relative proportions of the other ingredients or upon the molecular weight of the polyesters. It can be seen, therefore, that the flexibility or stiflness of the resulting copolymer can be varied simply by varying molar ratios of the components thereof and/or by employing components of varying molecular weight.

The use of blends of elastomeric copolymers, as set forth hereinabove, enables the heat setting step of my process to be applied to blends including up to 50% by weight of soft copolymers, said copolymers being unable to withstand, [by themselves, the temperatures usually employed in the heat setting step. Usually, the soft copolymers are unstable as fibers at temperatures of above 75 C. and have even disintegrated on the bobbin at tem* peratures of about 100 C. The stifi' copolymers alone are generally stable as fibers up to temperatures of at least 200 C. It should also be noted that the solvent treatment of my process enables some polymer blends to withstand heat treatment, whereas these blends, without such solvent treatment, would be unstable when exposed to the temperature of the heat setting step.

Furthermore the characteristics possessed by a fiber spun from a blend are usually superior to those of a fiber spun from a single copolymer of comparable chemical composition. More specifically, a blend of a stiff copolymer obtained by reacting given quantities of certain reactants and a flexible copolymer obtained by reacting other given quantities of certain reactants in the manner described above yields a fiber having more desirable characteristics than a fiber produced from a single copolymer obtained by reacting together the same quantities of all of the reactants employed to produce the stiff and the flexible copolymers.

In summary, I have discovered a means to advantageously alter the tensile properties and molecular fine structure of elastomeric fibers. It is believed that the action of the swelling solvent on the fibers, accompanied by high stress, promotes mobility of the amorphous fiber regions, resulting an in improved molecular arrangement in the fiber. Swelling solvent treatment of these fibers also imparts thereto a higher order of molecular registration and a higher degree of fiber tenacity.

The embodiments of my inventions will be further illustrated in the following examples. In each of the examples permanent set was determined by the same method unless otherwise indicated. Briefly, all samples were conditioned for 24 hours at 65% relative humidity and 23 C. prior to testing. Each sample was then marked while in a taut (not stretched) state, so that four marks appear on the fibers, the distance between the outer marks being 5.00" and the distance between the inner marks being 3.00. The sample was then clamped between jaws set so that the 5 tested length lay between the jaws. The jaws were then moved about so that the same was extended until the distance between the inner marks (3" before extension) were:

12.00" for a 300% extension 8.00" for a 200% extension 6.00" for a 100% extension Length after extension-3.00

X 100=percent set EXAMPLE I In this example and the examples that follow, two principal types of polyesterurethane copolymers were utilized. These copolymers, hereinafter designated as copolymer A and copolymer B, were prepared as follows:

Copolymer A A polyesterurethane copolymer of the type described in U.S. Pat. 2,871,218 was obtained by reacting hydroxyl poly(tetramethylene adipate) (molecular weight=l0l0, hydroxyl number=106.l), butanediol-l,4, and diphenyl methane-p,p-diisocyanate in a molar ratio of about 1:1:2, respectively.

Properties of copolymer A Hardness (Shore A): Relative viscosity (25 C., 0.4 g./ ml. DMF):

1.36 Brittle point (ASTM-below D 746): --10l F.

Copolymer B A polyesterurethane copolymer of the type described in US. Pat. 2,871,218 was obtained by reacting hydroxyl poly(tetramethylene adipate) (molecular weight=850,

hydroxyl number=l30.4, acid number=0.89), butanedio1-l,4, and diphenyl methane-p,p-diisocyanate in a molar ratio of about l.0:0.3:l.3, respectively.

Properties of copolymer B Hardness (Shore A): 65 Relative viscosity (25 C., 0.4 g./l ml. DMF):

1.50 Brittle point (ASTMbelow D 746): -101 F.

A 30% solution in acetone of the copolymer being tested was employed to dry spin an elastomeric fiber. The apparatus used was of the type traditionally employed in the art and essentially included a spinnerette at the upper end of a spinning-column and a godet roll at the bottom of the column. The filaments were passed through the column where the solvent was substantially evaporated therefrom by contact with hot air introduced at a temperature of 150 C. and was then passed about the godet roll moving at a velocity of 20 meters/minute. The as spun yarn was wound on perforated bobbins at various levels of strain and immersed in containers filled with a swelling solvent. After 20 minutes contact time at 25 C. bath temperature, the bobbins were removed from the bath and allowed to dry at room temperature before being tested.

The following table sets forth the solvent systems employed to treat various elastomer fibers, and the properties imparted to these fibers by such treatment, as well as comparing the thus treated fibers with fibers not treated by my procedure.

The following table sets forth the results attained when fibers treated with the swelling solvents are subsequently heat treated. In all instances fibers spun from copolymer A were utilized and the fiber was stretched 3 times its original length. The permanent set was determined after exposure to boiling Water for 30 minutes.

TABLE II Solvent system Methanol] methylene chloride (vol. percent) Permanent set after boil-oil (percent) Stretch during Treatment 1 solvent treatment 1 ST Solvent treated; HS Heat set.

TABLE I Properties of Solvent Treated Fibers Compared with Parent Yarn Properties Solvent system Methanol/ methylene Stretch chloride (v01. Copolymer during Permanent Treatment 1 percent) Stretch during treatment tested spinning 1 set (percent) 50/50 100% A 3 16 0/100 A 3 l6 100/0 A 3 20 A 3 20 /75 A 3 B: Acetone/Water (vol. percent) 70 100 A 1 26 A 1 30 30/70 1007 A 3 30 As spun in A 3 30 100/0 100%.. A 3 19 /50 100%.. A 3 25 25/75 100%. A 3 2.) 0/100 100% A 3 34 As spun A 3 26 100 0 Role 50%A/50%B 3 3 19 100%. 50%A/507 B a 3 Broke 25 {Relaxed 50%A/50%B 3 3 25 100% 50%A/50%B a a Broke R axed 50%A/50%B 3 3 28 50/50 Constant length 50%11/50%B 3 3 27 100% 50%A/50%B 3 3 17 25/75 100% 50%A/50%B 3 3 10 0/100 100%.. 50%A/50%B, 3 21 As spun 50%A/50%B 3 3 45 l ST=solvent treated. 2 Times the original length. 3 Weight percent.

EXAMPLE II EXAMPLE III The procedure of Example I was followed with the exception that the elastomeric fiber, after being treated with a swelling solvent under various levels of strain and dried in air at room temperature for 24 hours, was then placed at constant length in a hot air convection oven maintained at 110 C. for about 10 hours.

The procedure of Example I was followed to spin fibers formed from copolymer A. The following table illustrates the effect of stress during solvent treatment and shows that, with increasing strain, the elongation decreases and tenacity increases. In all instances, the fibers were stretched during spinning three times their original length.

TABLE III Physical properties of solvent treated fibers (Methanol/Methylene chloride system) Boiled-ofi properties Solvent treated Solvent treated and heat set Stress Stress Bath comp. Stretch, P.S., Elong., 'Ien. at 300%, P.S., Elong, Ten., at 300%, MeOH/MeCh percent percent Denier percent g./d'. g./d. percent Denier percent g./d. g./d.

R 30 160 500 0. 70 0. 19 100/0 -{C.L. 29 172 510 0.76 0. 20 100 29 160 450 0. 67 0. 20 (it it tit 23% 8'23 8'32 5o 23 100 21 130 400 0.81 0. 33 150 22 R 37 180 530 0. 67 0. 18 50/50 C.L 25 120 510 0, s2 0. 24 100 16 110 370 0. 80 0.46 25/75 Fiber dissolved (I; L C l 18:; 530 0.79 0.21

- 0a esee 0/100 50 19 100 16 95 370 0.83 150 18 Control fiber:

As spun 29 175 550 0.87 Heat set 18 89 420 0.91

N urn-Code: R= Relaxed; C.L.= Constant length; P.S.=Permanent set.

EXAMPLE IV This example illustrates the use of a blend of segmented copolymers in the process of this invention. The following table shows the eifect of solvent treatment on the permanent set of fibers spun from copolymer mixtures. In all instances, the fibers were stretched three times their length during spinning.

TABLE IV Permanent set Copolymer A] copoly- Strsin during mer B Copoly- Solvent system solvent treatment mixture 1 mer A Acetone/water (vol. percent):

100/0 Relaxed 19 25 4O Constant length 19 2 g 75/25 z a 50/50 {Constant length 27 22 28 20 25 27 iii .1 it 3% e axe 0/100 "{Constant length- 27 as 100% 21 34 As spun fiber 45 26 1 5 1 0 11 6 r i h r 'i ri g permanent set testing since they did not have the necessary 300% minimum elongation.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the invention as defined by the following claims.

What is claimed is:

1. A process for lowering the percent permanent set of a synthetic segmented polyurethane-based copolymer elastomeric fiber following extension of the fiber which comprises stretching the fiber, relaxing the fiber and contacting the fiber with a swelling solvent therefor to produce a swelling effect on said fiber while maintaining the fiber in a state of stress sufiicient to maintain the fiber at from about 0% to 150% strain and then heating the fiber at a temperature of from about 75 C. to a temperature below the softening point of the fiber.

2. A process for lowering the percent permanent set of a synthetic segmented polyurethane-based copolymer elastomeric fiber following extension of the fiber which comprises spinning a fiber from a synthetic segmented, polyurethane-based elastomeric copolymer, stretching the fiber, relaxing the fiber and contacting the fiber with a swelling solvent therefor to produce a swelling effect on said fiber while maintaining the fiber in a state of stress sufficient to maintain the fiber at from about 0% to about strain and then heating the fiber at a temperature of from about 75 C. to a temperature below the softening point of the fiber.

3. The process of claim 2, wherein said segmented, elastomeric copolymer is represented by the formula:

wherein H denotes the hard segment and S denotes the soft segment; and wherein H is further represented by wherein Q is a divalent radical derived by reaction of an organic diisocyanate with active-hydrogen containing functional groups; G is the residue resulting from the removal of active hydrogen from the terminal functional groups of a low molecular weight bifunctional molecule 'having a molecular weight less than 500; x is an integer from 0 to 1; b is an integer greater than zero; and wherein S is the residue resulting from the removal of the active hydrogen from the terminal functional groups of a polymer melting below 60 C. and having a molecular weight of from about 250 to about 5000.

4. The process of claim 3, wherein the fiber is stretched from about 200% to about 500% of the initial fiber length.

5. The process of claim 3 wherein the swelling solvent is selected from the group consisting of methanol, methylene chloride, chlorobenzene, nitrobenzene, acetone, methyl ethyl ketone, methanol-methylene chloride mixtures and acetone-water mixtures.

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